The present invention relates to a device for ventilating the middle ear by means of a ventilation tube which is made of a tissue-compatible material, preferably titanium, and which has a through-channel for air communication between the cavity of the middle ear and the outside air.
As is known, the function of the middle ear is to transmit sound energy from the environment to the inner ear, where the sound signals undergo complex processes of interpretation. This transmission of sound energy from the environment to the inner ear requires an impedance conversion of the sound signal, since the sound energy is being conveyed from one medium (air) to another medium (liquid) which is located in the inner ear and which has a considerably higher impedance than air. With the aid of the auditory ossicles and the shape of the surrounding organs, an impedance conversion takes place in the middle ear. A basic condition if normal hearing is to be maintained is that the normal impedance in the middle ear is retained and that the movement in the transmission chain is not damped, which necessitates a normally ventilated middle ear.
One of the commonest complaints seen in otology is, however, accumulation of liquid in the middle ear, which results in diminished hearing. This is especially common among children but also occurs in adults with chronic inflammation of the middle ear. Puncturing the tympanic membrane and fitting a ventilation tube is therefore a common operation. In the USA alone, approximately one million operations of this type are performed each year. In total, some 5 million ventilation tubes are used each year for these operations in Western Europe, the USA and Japan, most of these being performed on children under anaesthesia.
Some of these children with middle ear problems do not improve as they grow older, and instead the problems remain and become chronic in the adult years. The result is that the function of the middle ear is gradually destroyed. In most cases there is a progressive destruction of the middle ear, with consequently impaired hearing, gradually leading to severe hearing loss. These patients are normally helped initially by means of a tube through the tympanic membrane in a traditional manner, but the tube is expelled after a short time and the tympanic membrane becomes more and more damaged by these repeated treatments, and for this reason the method does not help the patient in the long run. It would therefore be desirable to devise a method by which it is possible to ensure ventilation of the tympanic membrane in these patients too.
A standard procedure here is the restoration of the middle ear, which involves removing excess connective tissue and enlarging the middle ear by excising bone, primarily in the mastoid area. This surgery increases the chances of the patient acquiring better hearing, but it has to be combined with an air channel for successful results. The surgical intervention is relatively extensive and cannot be repeated simply to make a diagnosis of the condition of the middle ear. It would therefore be desirable to have access to a channel which is large enough to accommodate a fibre optic instrument for examining the condition of the middle ear.
Where the normal method of ventilation via the tympanic membrane cannot be used, other methods have been tried, among others ventilation lines through the Eustachian tube or ventilation tubes at the margin of the tympanic membrane, i.e. between bone and soft tissue. However, none of these methods has been successful and come into general use.
With the aim of reducing the risk of expulsion and thus avoiding repeated surgical interventions, it is also already known to design the ventilation tube in the tympanic membrane with an outer surface made of titanium. The metal titanium has, as is known, been found to have unique properties of biocompatability with the body tissues. Different areas of clinical application have been tried out with success. Fixtures of various types which are anchored in the bone are used to secure various types of prostheses, for example dental prostheses in the jawbone of the oral cavity, and hearing aids anchored in the bone of the skull. In both cases, the titanium surface adapts extremely well both to the bone tissue and also, respectively, to the mucous membrane of the oral cavity or the skin.
The metal titanium, with its excellent biocompatibility properties, has also been shown to have relatively high affinity for binding blood products and forming tissue even on surfaces which are not primarily in contact with tissue. Among other things, this has led to ventilation tubes, placed in the tympanic membrane, becoming blocked more easily if they are made of titanium rather than of polymer material. In addition, a tube fitted in the tympanic membrane is in practice impossible to clean since the tympanic membrane is sensitive to contact.
Swedish Patent Application 8703694-3 describes a ventilation tube for temporary healing into the tympanic membrane, which consists of a plastic tube whose outer side has been provided with a continuous coating of titanium oxide. Alternatively, the ventilation tube can consist of a titanium tube whose inner air channel has been treated with a layer which annuls titanium""s normal affinity for body secretions and body tissues, with the aim of preventing blockage of the ventilation channel.
Although the described ventilation tube has advantages over conventional ventilation tubes made of titanium, this type of ventilation tube does not represent a solution in those cases where a permanent anchoring is sought. In this case too, a certain amount of blockage of the ventilation channel takes place sooner or later, and this makes cleaning necessary.
Especially in the case of adults with chronic inflammation of the middle ear, there is at the present time no satisfactory method for obtaining the desired ventilation of the middle ear.
The aim of the present invention is to remedy the difficulties described hereinabove and to create a permanent ventilation channel for the middle ear.